Polyester materials are widely used as extrusion and injection molding resins for applications such as fibers, films, automotive parts, food and beverage containers and the like. Commonly used polyesters include poly(ethylene terephthalate) (PET), poly(1,4-butylene terephthalate) (PBT), and poly(1,4-cyclohexylenedimethylene terephthalate) (PCT). These crystallizable polymers generally have good heat resistance and high glass transition temperatures. However, they sometimes show crystallization-induced brittleness during extrusion and thermoforming operations, especially when loaded with high concentrations of fillers such as carbon black, talc and the like.
Conductive polymers are known to be useful for packaging materials for packaging of electrostatic sensitive electronic components.
Conductive polymers are particularly useful in the tape and reel market for packaging of electrostatic sensitive electronic components. For example, heavily filled polymer compositions based on poly(vinyl chloride) (PVC), polycarbonate, and high impact polystyrene have been evaluated for this application. The optimum fitness-for-use criteria for this market include electrostatic dissipation properties, dimensional stability, acceptable slitting characteristics, peelable seal characteristics to cover tapes, and low migration levels of condensable materials from the package to the packaged components. Conductive high impact polystyrene and PVC compositions are deficient in impact strength and sealing characteristics. The poor environmental image of PVC is also detrimental to its use in this application. Polycarbonate compositions are expensive and have impact problems as well as sheet drying requirements prior to thermoforming operations. Therefore, there is a need for a conductive polymer which overcomes the above described deficiencies.
WO 91/10237 discloses an anti-static composition containing conductive polymers with increased conductivity from at least one non-conductive matrix polymer and at least two additives. In one of the examples, copolyester of poly(ethylene terephthalate) containing cyclohexanedimethanol and ethylene glycol combined with polyaniline is shown. This disclosure does not show the use of carbon black or impact modifiers, either singly or in combination with the conductive copolyester.
U.S. Pat. No. 4,876,033 (1989) assigned to Bayer A. G. discloses molding resins based on blends of polycarbonate, a poly(alkylene terephthalate) such as PET, PBT, or PCT, carbon black, and graphite.
U.S. Pat. No. 4,699,942 (1987) assigned to Eastman Kodak Company discloses molding compositions based on PET, a low molecular weight polyethylene mold release agent, talc, carbon black, a hindered phenolic antioxidant and optionally reinforcing glass fibers.
U.S. Pat. No. 4,559,164 (1985) assigned to General Electric Company discloses a plastic composition characterized by electroconductivity and comprising up to 90 weight per cent PBT, carbon black, and from 1 to 50 weight per cent of a Bisphenol A polycarbonate, glass fibers and/or rubbery polymers. Although these crystalline PBT-based blends have desirable elctroconductivity properties, extruded sheets are brittle in the machine direction and they are difficult to thermoform into desired shapes.
U.S. Pat. No. 4,369,282 (1983) assigned to General Electric Company--This patent describes modified thermoplastic polyester compositions which comprise a PBT resin, optionally a PET resin, a modifier comprising a combination of a polyacrylate resin or a vinyl aromatic-diene block copolymer resin and a poly(1,3-butylene terephthalate) resin and optionally a filler and/or reinforcing agent and/or a flame retardant. Such compositions do not contain carbon black and would not be suitable for applications requiring electroconductivity.
U.S. Pat. No. 4,267,286 (1981) assigned to General Electric Company--This patent describes thermoplastic polyester compositions based on PBT which are similar in composition to those described in U.S. Pat. No. 4,369,282. Again, the compositions contain no carbon black and are not suitable for applications requiring electroconductivity.
U.S. Pat. No. 4,554,314 (1985) assigned to Mobay Chemical Corp. discloses thermoplastic molding compositions which are blends of poly(alkylene terephthalate) and polycarbonate resins containing shell/core graft modified polybutadiene rubber modifiers. The compositions contain no carbon black and are not suitable for applications requiring electroconductivity.
None of the above described references solve all of the numerous problems in the art of lack of appropriate electroconductivity, brittleness, difficulty in thermoforming into desired shapes, deficiencies in impact strength and sealing characteristics, poor environmental image, and impact strength problems. Therefore, there is a need in the art for a conductive polymer which overcomes the above described deficiencies.